The present invention relates, in general, to field emission displays and, more particularly, to methods and circuits for maintaining a substantially constant brightness of the field emission displays over temperature.
Field emission displays (FED""s) are well known in the art. A field emission display includes an anode plate and a cathode plate that define a thin envelope. Electron emitters are disposed on the cathode plate and conduct an electron emission current to the anode plate. To control the electron emission current, ballast resistors are provided between the electron emitters and the cathodes. The ballast resistors function to limit the electron emission current through each of the electron emitters and the cathodes. The FED generally requires high resistivity ballast resistors as part of the cathode design. The high resistivity materials used for ballast resistors are generally characterized by a large resistivity change as a function of temperature of the field emission display and cathode plate. This results in a very dramatic change in electron emission current over temperature for the FED when driven with a fixed voltage across the gate to cathode terminals, and consequently, a dramatic change in brightness of the FED over temperature.
Likewise, the gate to cathode voltage could be adjusted during operation in order to fix the emission current. In this mode of operation the change in ballast resistance over temperature may require voltages in excess of the ability of either the drive electronics or the FED structure to operate reliably, thus reducing the practical temperature range achievable.
Accordingly, there exists a need for a method and circuitry for maintaining a substantially constant brightness in a field emission display over wider variations in temperature.